Examine source code of Word Counter - Sum Select

{
  "manifest_version": 2,
  "name": "Sum Select",
  "description": "Sum Select enriches browsing and editing. Highlight text and instantly get the word & char count with this simple Chrome extension.",
  "version": "1.0",
  "permissions": [
    "storage"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "images/icon16.png",
      "48": "images/icon48.png",
      "128": "images/icon128.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "tb@tarotmancer.com",
      "strict_min_version": "57.0"
    }
  }
}